Spotting after period

So I had my period from the 14th- 21st of this month . But 4 days later I started spotting pink discharge (which was yesterday) and now today I’ve been lightly spotting darker red and kinda cramping a bit. But not enough to bother me just enough to notice it’s happening. And on the 10th I had sex but we used a condom..... and I started taking my birth control pill on the 9th... I’m not sure what’s going on but if someone could give me some inside that’d be great :)